1. Field of the Invention
The present invention relates to printing methods, computer-readable media, printing apparatuses, methods for manufacturing printing apparatuses, printing systems, and correction patterns.
2. Description of the Related Art
Color inkjet printers (hereinafter referred to as “printers”) that eject inks of a plurality of color onto a medium such as paper to form an image are known as printing apparatuses. These printers repeat in alternation a dot formation operation of forming dots on a paper by ejecting ink from a plurality of nozzles, which move in the movement direction of a carriage, and a carrying operation of carrying the paper in an intersecting direction (hereinafter, also referred to as the “carrying direction”) that intersects the movement direction using a carry unit. By doing this, a plurality of raster lines each made of a plurality of dots aligned in the movement direction are formed in the intersecting direction, printing an image.
With this type of printer, there are variations in the ink droplet ejection characteristics, such as the amount of the ink droplet and the travel direction, for each nozzle. Discrepancies in the ejection characteristics are a cause of darkness non-uniformities in printed images, and thus are not preferable. In conventional countermeasures, correction patterns are first printed on the paper using each of the respective color inks that are ejectable. Next, the darknesses of the printed correction patterns are read, correction information is obtained based on the data that had been read, and printing is carried out by executing darkness correction based on the obtained correction information.
(1) In conventional methods, correction patterns are printed using each ejectable color ink, the printed correction patterns are then read, and darkness correction is carried out based on the data that has been read. That is, if four color inks are ejectable, then four correction patterns are printed for those colors, and if six color inks are ejectable, then six correction patterns are printed for those colors. However, depending on the ink color, there are colors in which darkness non-uniformities have a tendency to occur (colors in which darkness non-uniformity is easily visible) and colors in which it is difficult for darkness non-uniformities to occur (colors in which darkness non-uniformity is not easily visible). For this reason, there is little effect in carrying out darkness correction for a color in which it is difficult for darkness non-uniformities to occur. That is, notwithstanding the large amount of time spent in processes such as the process of printing a correction pattern using a color in which it is difficult for darkness non-uniformities to occur, the process of reading the correction pattern of the color in which it is difficult for darkness non-uniformities to occur, the process of obtaining correction information based on the data that has been read for the color in which it is difficult for darkness non-uniformities to occur, and the process of carrying out darkness correction based on the obtained correction information for the color in which it is difficult for darkness non-uniformities to occur, there is little effect in darkness correction for the color in which it is difficult for darkness non-uniformities to occur. And for this reason, a large amount effort and time is wasted by carrying out darkness correction for a color in which it is difficult for darkness non-uniformities to occur, such that there is a problem of reducing the throughput of the printer.
(2) Furthermore, in carrying out darkness correction, a large amount of time and effort is spent in processes such as the process of printing a correction pattern, the process of reading the correction pattern, and the process of carrying out darkness correction based on the data that is read. Conversely, by omitting darkness correction in regions in which there is little effect, it would be possible to restrain the effort and time wasted on these.
In this regard, darkness non-uniformities tend to occur easily in light regions within a printed image. For example, when printing portrait images, the darkness of the printed image is light in regions in which human skin colors are rendered, and therefore darkness non-uniformities tend to occur easily. For this reason, the effect of darkness correction is easily obtainable in regions of light darkness. On the other hand, darkness non-uniformities tend not to occur easily in dark regions within a printed image, and there is little effect in carrying out darkness correction.